The present invention relates to a fiber composite crash structure for a motor vehicle longitudinal member and the like, and more particularly, to a fiber composite produced at least partially from fiber composite material.
Crash structures, deformation elements and energy absorbers are used in vehicle and aircraft construction and in train and helicopter engineering in diverse structural forms and at different points in order to increase the safety. These energy-absorbing components consist, for example, of steel or aluminum sheet or of aluminum extruded profiles. Moreover, fiber composite materials have increasingly been used recently, primarily owing to the weight-saving possibility which is associated therewith.
In motor vehicles, deformation elements having a tubular construction have proven successful in particular in the front and rear regions. A tubular structure of this type is disclosed, for example, in DE 30 49 425 A1. In this case, the crash protective component, which is designed as an open hollow body, has a circumferential surface in the form of netting made of a fiber composite strand for the irreversible absorption of energy in the event of pressure loads in the longitudinal direction. At small pressure loads in the longitudinal direction of the tube, the tube is used for an elastic, reversible support and, at relatively large loads, irreversibly absorbs energy under permanent deformation.
Furthermore, DE 38 33 048 A1 describes a bumper for motor vehicles, which has conically arranged impact tubes made of at least one fiber composite material. The impact tubes, which are arranged conically with respect to one another at a radial distance, are arranged in such a manner that their longitudinal axis extends at least approximately in the longitudinal direction of the vehicle, and therefore in the direction of travel, with the fibers being aligned at least essentially in the longitudinal direction of the tube. Glass fibers, carbon fibers or aramide fibers are used as the fibers.
In addition, DE 43 17 738 A1 discloses an energy absorber which is of cylindrical design and is composed of fiber-reinforced composite material, in which the fiber is wound at least in a circumferential direction of the body. Furthermore, the thickness of the energy absorber, which is of hollow-shaped design, is designed such that it increases gradually in at least two steps in the axial direction.
Furthermore, EP 0 683 072 B1 describes a further, hollow-shaped impact absorber which has the shape of a stepped pyramid or its circumferential surfaces are of terrace-shape design. The energy absorption takes place here predominantly by way of successive shearing processes. The material of the impact absorber consists of fiber material which has been compressed in a dimensionally stable manner.
The known arrangements largely have the disadvantage, however, that a high energy absorption capacity is possible only at a 0 degree impact. If, in contrast, the impact acts at an angle with respect to the longitudinal direction of the absorber element, then a uniform failure behavior does not occur.
It is also disadvantageous that known arrangements only have a low structural integrity. That is, the structure splits into large broken fragments during absorption of the impact energy. Broken fragments of this type constitute, however, a high injury risk and are therefore undesirable.
Furthermore, the crash behavior of the known structures can be calculated only imprecisely, and a high outlay on experimentation is required in order to predict that behavior.
In addition, in many components made of fiber composite material, the production is associated with a high proportion of manual labor, since 3D structures have to be manufactured from sheet-like semifinished fiber composite products. This entails, as a rule, not only a large amount of cutting of the sheet-like semifinished product, but also results in slow and therefore expensive manufacturing.
The present invention is based on the object of providing a fiber composite crash structure with reproducible crash behavior and optimum structure integrity which, in addition, can be produced cost-effectively.
According to a first embodiment, the object has been achieved by a fiber composite crash structure which has a hollow body produced entirely or partially from fiber composite material. The structure is distinguished according to the invention in that, within the hollow body, a web element is arranged running essentially in the longitudinal direction thereof. The web element is connected to the hollow body essentially in the contact region of web element and hollow body in such a manner that the structure is reinforced by reinforcing elements.
In this embodiment, the hollow body has any desired cross section. It is expedient, however, for the cross section to have an oblong, oval, elliptical, circular or polygonal shape.
A second embodiment of the fiber composite crash structure according to the invention, in which the web element can be omitted, is distinguished in that the hollow body has a circular cross section. Reinforcing elements are introduced into the hollow body wall in order to reinforce the structure.
In addition to the weight reduction, the crash structure according to the invention made of fiber composite material has the advantage of a high specific energy absorption. Even in the case of an oblique impact, the component has high structural integrity and optimum crash behavior. In addition, the absorption behavior can be readily predicted and adapted in a simple manner to desired requirements.
The reinforcing elements are advantageously arranged running essentially in the thickness direction of the hollow body wall. Owing to the orientation of the reinforcing elements, the shock acting on the structure is optimally absorbed and, in particular, the absorption of energy in the case of an oblique impact is substantially improved. In addition, a structure reinforced in such a manner has a better structural integrity. As a result, in the event of a crash, spitting off or spitting up of broken fragments is avoided.
Furthermore, it is expedient to arrange the reinforcing elements in a manner such that they run entirely or in sections in the circumferential direction of the hollow body and along the longitudinal direction thereof.
It is particularly advantageous that the distance between the reinforcing elements both in the circumferential direction of the hollow body and in the longitudinal direction thereof can be set in a variable manner in order to adapt the energy absorption capability of the structure. That is, the absorption behavior can be adapted in a simple manner, by varying the density of the reinforcing elements to a desired force/distance profile. It is advantageous in this respect, since in contrast to known structures, no new design, and therefore also no new tools for producing the structure, are required when adapting the absorption behavior. This constitutes an extremely effective form of adaptation saving on both costs and time.
The reinforcing elements are expediently sewn into the hollow body wall by tufting, and the web element and the hollow body are sewn to each other essentially in the contact region by tufting. The sewing process has the advantage of easy handling capability. In addition, it can easily be integrated in automated production sequences. Thereby, at least partially automated manufacturing is possible, so that shorter manufacturing times and lower outlay on personnel are required, which results in a significant cost reductions.
The reinforcing elements are expediently sewing threads comprising glass and aramide fibers, the use of glass fibers being more cost-effective.
Moreover, it is advantageous that the hollow body has a conical shape in the longitudinal direction and has a variable wall thickness which is of step-shaped design in the longitudinal direction. As an alternative, the hollow body can have a wall thickness continuously increasing in the longitudinal direction. As a result, the level of maximum force application is set in a known manner, so that a restraint system is realized using simple techniques.
According to a particularly currently preferred embodiment, the hollow body comprises a fiber composite mesh. The use of a fiber composite mesh is expedient owing to the manufacturing which is close to final contours and is automated. In this case, cutting, as is the case, for example, when other 2D multiaxial structures or fabrics are used, scarcely occurs, so that the material costs are reduced. The partially automated manufacturing also results in shorter manufacturing times with a lower outlay in personnel.
In the case of the embodiment having a web element, the latter expediently has a double T-profile. The T-shaped sections of the web element are connected to one another via a central region, and the T-shaped sections connecting the more closely adjacent, opposite side surfaces of the hollow body to each other. Great stability is thereby imparted to the crash structure.
It is furthermore advantageous that the web element, like the hollow body, consists of fiber composite material. In this case, it is particularly expedient that the web element consists of a sewn-up multiaxial structure, with the fiber alignments of the multiaxial structure having an angle of 45xc2x0 with respect to the longitudinal extent. The use of a multiaxial structure makes possible an arrangement in which the force lines are so orientated. The 45xc2x0 orientation results in optimum sheer strength and ensures complete functioning capability of the entire system even in the case of an angular impact (oblique impact). In addition, a T-profile web of this type comprising a multiaxial structure can be produced relatively simply and cost-effectively.
The crash structure according to the invention is preferably used as a crash longitudinal member in a passenger vehicle. Moreover, the fiber composite crash structure can be used as a deformation element in an aircraft, a helicopter or a rail vehicle.